Spectroscopic Characterization Of Radiation Induced Defects In Gallium Nitride

Author : Anup Sasikumar
Publisher :
ISBN 13 :
Total Pages : 215 pages
Book Rating : 4.:/5 (98 download)

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Download or read book Quantitative Spectroscopy of Reliability Limiting Traps in Operational Gallium Nitride Based Transistors Using Thermal and Optical Methods written by Anup Sasikumar and published by . This book was released on 2014 with total page 215 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gallium nitride (GaN) based high electron mobility transistors (HEMTs) have shown a lot of promise in high voltage, high power, and high radiation applications. However the full realization of the III-nitride potential and large scale adoption of this technology has been hindered by the existence of electrically active defects that manifest as deep levels in the energy bandgap. These deep levels can potentially act as charge trapping centers limiting device performance and long term reliability. It is therefore imperative to monitor these traps in operational GaN HEMTs as close as possible to their real world operational conditions. With that goal in mind, in this dissertation, a suite of advanced thermal and optical based trap spectroscopy methods and models collectively known as constant drain current deep level (thermal) transient spectroscopy and deep level optical spectroscopy (CID-DLTS/DLOS) were developed and expanded upon to directly probe and track traps in three terminal operational GaN HEMTs. These techniques have allowed an unprecedented ability to quantitatively track trap levels throughout the wide bandgap of operational GaN devices. Depending on their mode of switching (gate-controlled versus drain-controlled) the techniques are able to distinguish between under gate and access region defects irrespective of device design and/or operational history. The devices studied here were subjected to a range of different stressors and very different trap induced degradation mechanisms were identified that further confirms the need for such high resolution defect spectroscopic studies in GaN HEMTs. Specifically the GaN HEMTs studied here were subjected to three very different kinds of stressors, i) high frequency moderate drain voltage (50 V) accelerated lifetime stressor were applied to GaN HEMTs optimized for radio frequency (RF) applications, ii) very high off-state drain voltage (up to 600 V) stressors were applied to GaN-on-Si MISHEMTs optimized for power switching applications, and iii) high energy particle irradiation (in this case 1.8 MeV protons) stressor applied to high frequency GaN HEMTs targeted for RF space applications. In the case of the RF accelerated electrical life testing, the GaN HEMTs over an array of different suppliers (mostly commercial) showed the signature of a EC-0.57 eV trap that was was identified as occurring almost ubiquitously. This trap was determined to be causing knee-walkout degradation, drain-lag and linked directly to RF output power loss through its trapping/detrapping activity in the drain access region. This level was unambiguously located in the GaN buffer using a combination of CID-DLTS, and supporting nano-scale DLTS/DLOS approaches. It was observed that the detection of this buffer trap was observed to be highly dependent on the reverse gate leakage of the GaN HEMTs and an empirical leakage based filling model was proposed to describe the electron capture process in HEMTs with leakage (10-7 A/mm). In contrast, for GaN HEMTs with very low reverse gate leakage (